Effect of multistage lamellar microstructure on mechanical properties of Tc18 alloy

Abstract

In this study, a three-step heat treatment approach, which included annealing, solution treatment at 740–820 °C, and aging at 450–550 °C, was employed to control the precipitation behavior of the α phase in TC18(Ti-5Al-5Mo-5 V-1Cr-1Fe) alloy. The multistage microstructure resulting was found to contain both the primary lamellar structure (α) and the secondary lamellar structure (αs), and the relationship between the spacing of multi-level lamellar microstructure and the mechanical properties of the alloy was effeciently determined. The study demonstrates that lowering the solid solution temperature reduces the interlayer spacing of the primary α phase, and increasing the aging temperature enlarges the interlayer spacing of the secondary αs phase, thereby enhancing the material's mechanical performance. Nevertheless, a substantial discrepancy in yield strength exists between these two interlayer spacings, which impacts the stress-strain coordination and reduces the plastic zone at the crack tip, and also increases the likelihood of formation of microvoids and microcracks at grain boundaries.